I have a 20 gallon tank with a huge canister filter with out put rate of 300 Gallons per hour, filled with carbon, sponge and some floss currently, the aquarium is fully cycles with 15 lbs of live rocks, and now I have a clown fish as well as an anemone in there now. today I decided to add sand to the bottom of the tank (to make it look better and more biological filteration). can anyone give me some pointers on how to add this ? should I remove the fish ? will it have to go through cycle again or it will just become live ?

furthermore, I have a UV light as well as a protein skimmer (which is essentially only an air pump since the skimmer is too cheap and doesn't work in my opinion), what kinds of chemical resins can I use in the canister to make up for the lack of skimmer ?_________________65 Gallon tank FW
1 shovel-nose catfish
1 Motoro Stingray
20 Gallon SW
2 clown fish
1 blenny
3 anemones
3 coral

Great job on the set up. I like the fact that you are using a UV. I have had great success with UV Sterilizers and consider them to be a very valuable addition to a marine aquarium.

The lack of a Protein Skimmer on a 20 gallon aquarium is not a big deal. Keep in mind, skimmers remove organic acids from the water. Inside your canister, to make up for the lack of a skimmer, you want a resin that absorbs organics from the water. The answer is simple... activated carbon. You should very aggressively use activated carbon, and completely replace the carbon every 3 to 4 weeks.

Just as important will be the cleaning of the filter pad inside your canister. This needs to be done every 2 or 3 days, twice weekly at MINIMUM. Filter pads trap detritus, causing nitrate and phosphate buildups, as well as a depletion of carbonates. All of these things tend to spiral out of control on systems without skimmers, so it is even more critical for you to clean the filter pads frequently.

As for sand, yes you can add sand to an established system. The biggest concern will be the dust that tends to accumulate. I would suggest buying an expensive reef grade live sand. Some brands are guaranteed not to cloud the water, but I would test it first outside the aquarium. You can use a net, held over a bucket, and drain some aquarium water through the sand to see if it clouds.

thanks a lot for your reply, I didn't know I should be cleaning the pads that often, will sure get on it today, do you recommend changing the whole sponge and floss I have in the canister ? or rinse them with de-chlorinated water would be enough ?

I have another quick question which I will ask here, my anemone last night kind of went into hiding under one of the live rocks, (out of display so I can't see him that much no more) should I be worried ? or is he just roaming around ? I leave my 2x10watt reef blue light on for 12 hours a day, and I'm not sure if the anemone is hiding from too much light !_________________65 Gallon tank FW
1 shovel-nose catfish
1 Motoro Stingray
20 Gallon SW
2 clown fish
1 blenny
3 anemones
3 coral

Your anemone is displaying normal anemone behavior. They will often move around until they find a comfortable area with the water flow and lighting they desire. By the way, be prepared for a difficult experience. Anemones are extremely difficult to maintain long term and the success rate in this hobby is embarrassingly poor. Very few animals live longer than 2 years, and the natural life span is over 200 years.

For the filter pads, I would rinse them in tap water so long as they hold up well, replacing them when necessary. This assumes you plan to keep them. Personally, I do not use mechanical filtration on my reef systems.